Cohousing is designed to facilitate shared responsibilities for child care, meals, and driving. And because projects are designed by residents, they are built to reduce energy and maintenance costs. For environmental reasons, some groups also maximize their use of sustainable building materials.

Twenty-four cohousing communities currently exist in the United States and 16 more are under construction. Typically, a community consists of 20 to 40 homes clustered around a courtyard or along a pedestrian street. Parking lots and preserved open space are often located at the edge of the community. Individual homes are usually equipped with full kitchens, but they have small floor areas because residents use a large common building, or common house, for group meals and recreation.

Along with a large kitchen and dining room, the common house may include lounges, guest rooms, offices, a laundry room, craft rooms, workshops, and rooms for children and teens.

Three recently completed communities have used particularly innovative techniques to conserve indoor energy. The Nyland community, in Lafayette, Colorado, uses passive solar design and water-conserving landscaping. The Ecovillage at Ithaca (EVI), in upstate New York, uses shared HVAC systems to maximize return on high-efficiency systems. And in Berkeley, California, an urban infill cohousing development uses nontoxic, sustainable building materials with minimal embedded energy.

These solar-heated Ecovillage houses in Ithaca, New York use vine trellises to mitigate summer sun. The roof orientation of the houses was also designed to accomodate the installation of photovoltaic cells.

Nyland Community: Dense and Efficient
Completed in 1993, the Nyland Community has 42 homes on about 6 acres, with 20 acres of shared open space, a solar-heated greenhouse, a workshop, and a 6,000 ft2 common house. The open space and common facilities are owned and managed by a homeowners' association. Because residents wanted their homes to be partially heated by solar radiation, the pedestrian streets run east/west, and the houses have a north/south orientation. This is unusual in developments on Colorado's Front Range, where most houses are built to capture the spectacular mountain views to the west without regard for overheating on summer afternoons.

Homes at Nyland have 2 x 6 optimum-framed walls insulated with wet-spray cellulose made mostly from recycled paper. Truss-joists were used in floors, and in roofs when cathedral ceilings ruled out truss roofs. The walls are R-24 and the ceilings R-42. Finished basement walls are insulated to R-13 and unfinished ones to R-5. To increase the whole-wall R-value, the insulation area was increased and lumber use reduced with optimum framing techniques, including 24-inch on-center framing and oriented strand board sheathing.

Most homes are clustered in groups of two or three under one roof, reducing the ratio of exterior wall area to interior air volume and decreasing the amount of structural lumber needed. Party walls have 2 inches of dead air space between insulated walls to decrease noise transmission. Similarly priced townhouses in the area have one 2 x 6 framed insulated wall separating adjoining houses.

All houses in the community have R-3 double-hung, double-pane, low-e windows rather than the R-2 thermal pane double-glazed windows typically found in similarly priced tract homes. The R-3 windows cost 20%­30% more than typical windows, but community members saved money by forgoing a primed exterior surface. This also allowed the members to paint the windows themselves, using a variety of colors.

The common house has forced-air heating divided among four separately controlled zones using electronically controlled duct dampers on a 90%-efficient gas furnace. The house incorporates high clerestory windows at the center of the building, eliminating the need for electric lighting in most parts of the building during the day.

Wonderland has monitored the devlopment's energy bills and compared them with average bills for Colorado homes of the same age and square footage. They have found that the Nyland homes use energy at only half the average rate. Data provided by the Public Service Company of Colorado (PSCO) indicate that Nyland homes use an average of 62% less natural gas and 33% less electricity than the average for Colorado homes built in 1988 and 1989.

The builders and designers of the Berkeley, California cohousing project recycled and reused a wide variety of materials in their building project. Much of the demolition material in the photo was reused in assembling new homes.

David Lowell and Kimeri Brown's 1440 ft2, three-bedroom house is typical of homes at Nyland. It has a total of 111 ft2 of south-facing glazing, or about 8% of the floor area. Since the home is part of a cluster of three units and its west wall adjoins a neighbor's home, the occupants opted for 104 ft2 of glazing to the east, but only 34 ft2 to the north.

Wonderland compared the Lowell/ Brown home with a computer-generated base case tract home. The base case has the same design, but minimum efficiency measures. The base case had a heating load of 36,000 Btu/ft2 per year, while the Lowell/Brown home requires only 26,000 Btu/ft2 per year, due to higher R-values and tighter construction. The solar gain resulting from the sun-tempered design lowers the heating load another 25% to 19,500 Btu/ft2 per year. The natural gas bill for space heating (separate from hot water and cooking) would be $198 per year, or 46% less than the $365 bill for a typical tract house.

Nyland won $100,000 in grants from the Colorado State Office of Energy Conservation and the Environmental Protection Agency for its commitment to energy conservation. Of this amount, $40,000 was designated for energy improvements to homes, $20,000 for energy improvements to the common house, and $40,000 for indoor air quality improvements.

This home at the Berkeley cohousing project included roofs made of fiberglass composite shingles (which are less toxic than asphalt), window overhangs, extra thermal mass in the form of 5/8 sheetrock walls, and gypcrete or tile floors.

Ithaca: Common Systems for the Common Good
Ecovillage at Ithaca (EVI) is on a 176-acre site, where 80% of the land is being preserved as agricultural open space, woods, and wetlands. EVI has an organic farm and one cohousing neighborhood, called the First Neighborhood; four more cohousing neighborhoods and an education center are planned.

The First Neighborhood's 30 homes include several costly energy efficiency measures. To conserve transportation energy, they are located close to the center of the city. They have passive solar design, superinsulation, tight construction, constant mechanical ventilation, energy-efficient appliances, and energy-conserving domestic hot water measures.

A particularly innovative aspect of the First Neighborhood is its shared heating and domestic hot water (DHW) system, which allows individual households to benefit from centralized efficient equipment, while still paying according to their energy use. The system was designed by Greg Thomas, an engineer and resident of the community. Each cluster of four to six houses has a pair of 83% efficient 200,000 Btu per hour Vaillant gas-burning boilers. These provide heat and DHW to the cluster.

The boilers pump hot water into an insulated piping loop. This loop travels between houses in underground chases made of 18-inch sewer pipe. For heating, each unit has a water-to-air heat exchanger and an air handler to pump hot air throughout the unit via indoor ducts.

Domestic hot water is also heated by the boiler loop. Each unit has a 20- or 30- gallon storage tank heated by the boiler loop water. The stored hot water increases the system's ability to respond to peak loads. The storage tanks don't have any backup system, but there have been no problems with residents running out of hot water.

Submetering prevents the typical problem of overutilization in multifamily boiler systems. Constant-flow valves control the loop flow to each unit. Run time meters are attached to the zone valves. Every two months, a resident reads the various meters and enters readings into a spreadsheet to produce heat and DHW bills for each unit.

The overall distribution efficiency of the current system has not been studied. Thomas suspects that efficiency would be higher with individual gas furnaces, but there are other advantages to the centralized system. In conventional construction, each cluster of homes would have six to eight individual furnaces or heat pumps. By using two boilers per cluster, EVI has minimized maintenance and replacement costs.

The central heating plants will make future fuel-switching easier and cheaper. Similarly, if the residents decide they want more efficient systems, having fewer units will reduce the marginal cost of the upgrade, shortening the payback time. For example, to install 90% annual fuel utilization efficiency (AFUE) boilers today would cost roughly $3,000 per cluster. A similar upgrade for an individual household would cost $600-$1,000 with a payback of 11-18 years. But in a cluster of eight homes, marginal costs drop, reducing the payback to roughly 7 years.

The centralized system allows several residents to share one meter, reducing fixed costs. New York State Electric and Gas charges residential customers a fixed monthly fee of $22.50 for the first 3 therms of gas and almost $1 per therm after that. By using just one utility meter (and several submeters) per cluster, residents pay for only 5 meters instead of 31. The 30 households profit from a combined savings of over $7,000 per year, just by sharing meters.

Easy system replacement may come in handy. After having spent considerable extra money on many aspects of the development, the group chose to save some on first costs in the mechanical system. Thomas now believes the system would run better with a larger number of 90%-efficient, low-mass boilers. He also recommends computerized instantaneous submetering, which would simplify diagnostics (see Data Loggers: An Interview with Some Heavy Users, HE May/June 1997, p. 37).

The underground sewer pipes that serve as chases have also proved useful. They originally carried pipes for boiler water, phone and electric lines, and submetering wiring. Later, they allowed residents to add Ethernet cables (high-speed internet wiring) to all the basements in just one weekend. Residents plan to eventually build a central solar DHW facility; the hot water pipes will also be installed in the chases.

Berkeley: Infill without Landfill
The Berkeley cohousing community is located in an urban area and was collectively planned and built. It is especially notable for having recycled and reused construction and demolition waste. It has been pulled together partly by renovating existing buildings and partly by building with salvaged, recycled, and sustainably produced products.

The development is located on a busy street within walking distance of mass transit, restaurants, shops, and parks. Three years ago, the group purchased a one-acre lot with five single family homes, one in such a sad state that the group chose to demolish it, reusing some of the materials. They renovated the four other buildings, converting single family homes to duplexes. Once they built four new duplexes, they had 14 units and a common house in nine buildings.

When renovating existing buildings and constructing new ones, the group used environmentally sound materials and design as much as possible. After salvaging bricks, tile, and lumber from the homes being demolished, they exchanged old sinks, toilets, and windows for windows and doors at a local salvage yard. They also salvaged and milled the dying acacia trees cut from the site and used the lumber for interior stairways. Further landscaping adjusted the site's grading to maximize natural storm water absorption, diverting the water from the city's storm sewer system.

The new houses' foundations are made from concrete with a 15% mixture of fly ash, a waste product from coal-fired power plants. The fly ash makes the concrete a stronger and more workable product, said Tom Lent, project coordinator for the development. Though fly ash is readily available, it is not included in concrete unless specified. The ash reduces the embedded energy of the material and improves quality without increasing cost.

The sills and the deck framing were made with wood treated with alkaline copper quaternium preservative, instead of ammoniacal copper arsenate or chromated copper arsenate, which are difficult to dispose of safely.

The Berkeley group did make some compromises. They investigated using straw as a building material. But they determined that straw bale walls would consume 100 ft2 or so in each unit, and they could not afford to sacrifice that much interior space. They still intend to build a straw bale sound wall to separate the complex from the busy street.

After ruling out straw bale construction, the group hoped to use sustainably harvested wood for framing and sheathing. This is wood that is grown and harvested in a way that minimizes ecosystem damage and gives forests a chance to continue producing at their natural level. However, sustainable plywood sheathing was unavailable, and sustainable Douglas fir framing could only be purchased milled to order and delivered green. Since the group did not have time to store and dry it, they ended up using commercial lumber. The group was able to get some sustainably harvested redwood for the decking and trim by using finger-jointed wood pieced together from smaller lengths.

The roofs are made from fiberglass composite shingles, which are less toxic than asphalt ones. Floorings include bamboo plank, salvaged hardwood, and a machiche laminate floating floor backed by a pad made from recycled tires. The machiche is certified as a sustainably harvested tropical hardwood.

The group chose wool carpet with jute backing. They considered using carpet made from recycled PET plastic, but decided against it because they were concerned about the pollution produced by recycling plastic, and about off-gassing from plastic carpets in homes. They painted the interiors with paint that had no volatile organic compounds (VOCs); the exteriors are painted with recycled paint. They used copper plumbing for water service, although for sewerage they cut costs by using polyvinyl chloride (PVC) pipes, which are more polluting to produce.

All the buildings were designed to have extensive south glazing and minimal glazing to the north. Because the houses are longer east-west, it was easy to provide daylighting while only using south windows with overhangs. To capture the solar heat gain, the buildings have extra thermal mass in the form of thick 5/8-inch drywall, 1 1/2-inch-thick lightweight concrete floors, and some tile floors.

While building codes only mandated insulation levels (R-11 walls, R-30 ceilings) in new additions, the old buildings were retrofitted with the same level. However, Lent emphasizes that the insulation is only as good as its installation. Crews left large voids in some places and over-packed the fiberglass in others in ways that would have cut the insulation effectiveness dramatically if not fixed, he said. Lent often went back and corrected mistakes in the work he had paid for. For example, one insulating crew ventilated a cathedral ceiling with the vents between the drywall and the insulation.

Coming Soon to a Town Near You
Despite the problems, the Berkeley project and others across the country show that housing can be designed and managed by residents, conserving energy on several fronts. And, beyond the considerable savings from passive solar design, shared energy systems, and use of environmentally sensitive building materials, cohousing has the potential to save energy and resources by transforming people from isolated consumers to good neighbors.
Resources
A Primer on Sustainable Building, Rocky Mountain Institute, Snowmass, Colorado, Phone:(970)927-3851